The present invention relates to a laminated FRP (fiber reinforced plastics) sound bar for percussive musical instruments, and more particularly relates to improvement in the mechanical property of a laminated FRP sound bar used for percussive musical instruments such as xylophones, marimbas and vibraphones.
Conventional use of wood for sound bars is inevitably accompanied with poor uniformity in material quality and seasonal variation in tone quality such as tone colour and tonal pitch.
The use of FRP as a substitute for wood has already been proposed. The invention of Japanese Patent Opening Sho. 59-19997 is one of such proposals. The FRP sound bar of this earlier proposal includes a number of voids elongated in the direction of the fiber orientation in the resin matrix in order to assume characteristic extension of sounds with mild and warm tone colours. In production, fibers or thin rods made of low melting point alloys, thermoplastic resins or thermomeltable materials are dispersed in a resin matrix in the direction of the fiber orientation and the resin matrix is heated to remove these fibers or rods through melting for formation of the above-described voids. This process, however, necessitates multi-staged operational steps which naturally results in high production cost.
In order to overcome this disadvantage, a new type of FRP sound bar was proposed in the US. patent application Ser. No. 736,569 filed on May 21, 1985 (the German patent application P3518032.3 filed on May 20, 1985 and the Dutch patent application No. 8501525 filed on May 29, 1985). The FRP sound bar of this earlier application has a laminated construction in which a number of reinforcing fibers are dispersed in a resin matrix and elongated in the longitudinal direction of the sound bar and a plurality of longitudinal pores are formed and almost uniformly distributed over the entire cross section of the sound bar. In production of such an FRP souud bar, a plate like FRP component is formed by orienting in a resin matrix a number of reinforcing fibers in its longitudinal direction, at least one array of longitudinal grooves are formed in the FRP component, a plurality of FRP components are laminated and bonded together to form a face-to-face combination and a cutout for tonal pitch adjustment is formed in one face of the face-to-face combination.
The use of such a laminated construction simplifies the production process greatly and, as a consequence, reduces the production cost remarkably.
In this laminated construction, one face of one plate like FRP component provided with the grooves is bonded to one flat face of an adjacent plate like FRP component. At bonding of such FRP components, it is highly difficult to coat the flat face with the proper amount of bonding material. Excessive coating partially clogs pores ultimately formed by the grooves to be closed by the flat face, thereby causing inter-pore variation in the vibration characteristics of the sound bar. Whereas insufficient coating lowers the bonding strength between adjacent FRP components, thereby marring uniformity of the product. In addition, the presence of the grooves in one face results in a smaller bonding surface and, as a consequence, low bonding strength between adjacent FRP components. As a result, when the sound bar is beaten during performance in a direction parallel to the faces bonded together, the adjacent FRP components tend to separate from each other, thereby lowering the mechanical strength of the sound bar.